CA2189200A1 - Apparatus for identifying fingerprints - Google Patents
Apparatus for identifying fingerprintsInfo
- Publication number
- CA2189200A1 CA2189200A1 CA 2189200 CA2189200A CA2189200A1 CA 2189200 A1 CA2189200 A1 CA 2189200A1 CA 2189200 CA2189200 CA 2189200 CA 2189200 A CA2189200 A CA 2189200A CA 2189200 A1 CA2189200 A1 CA 2189200A1
- Authority
- CA
- Canada
- Prior art keywords
- lens
- prism
- light
- image
- ccd array
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Abstract
A fingerprint identification device is provide that includes a light source for emitting light coupled to a transparent prism having a slant surface to which a fingerprint being identified is contacted and in which light from the light source is directed for creating a fingerprint image. A CCD array is disposed a distance from the transparent prism, for receiving an image from the prism. An inexpensive lens is spaced between the CCD array and the prism, for focusing light received from the prism onto the CCD so that an image can be detected. Conveniently a diaphragm is coated on the periphery of a face of the lens about its outer edge for preventing some of the light propagating from the prism in the direction of the lens, from reaching the CCD array.
Advantageously, providing the diaphragm on the lens lessens Gaussian distortion and increases depth of field, conveniently, the location of the diaphragm is fixed directly on the lens, obviating careful placement and affixing of a discrete diaphragm about a focal point of the lens.
Advantageously, providing the diaphragm on the lens lessens Gaussian distortion and increases depth of field, conveniently, the location of the diaphragm is fixed directly on the lens, obviating careful placement and affixing of a discrete diaphragm about a focal point of the lens.
Description
APPARATUS FOR IDENTIFYING FINGERPRINTS
Field of the Invention This invention relates to finge~ ll identification, and in particular to an optical a~dlus therefor.
Description of the Prior Art 1 o Various optical devices are known which employ pnsms upon which a finger whose print is to be identified is placed. Generally these systems rely on suitable optical components and adequate light for imAging. The prism has a first surface upon which a finger is placed. A second surface is disposed at an acute angle to the first surface through which the fingerprint is viewed and a third illumination surface through which light is directed into the prism. In some cases, the illul~lin-dlion surface is at an acute angle to the first surface, as seen for example, in US Patents 5,187,482 and 5,187,748.
In other cases, the illulllhldlion surface is parallel to the first surface, as seen for example, in US Patents 5,109,427 and 5,233,404.
Field of the Invention This invention relates to finge~ ll identification, and in particular to an optical a~dlus therefor.
Description of the Prior Art 1 o Various optical devices are known which employ pnsms upon which a finger whose print is to be identified is placed. Generally these systems rely on suitable optical components and adequate light for imAging. The prism has a first surface upon which a finger is placed. A second surface is disposed at an acute angle to the first surface through which the fingerprint is viewed and a third illumination surface through which light is directed into the prism. In some cases, the illul~lin-dlion surface is at an acute angle to the first surface, as seen for example, in US Patents 5,187,482 and 5,187,748.
In other cases, the illulllhldlion surface is parallel to the first surface, as seen for example, in US Patents 5,109,427 and 5,233,404.
2 o As fingerprint identification systems are becoming more in dernAn(l, their presence is increasing. One of the more basic and simple systems is shown in prior art Fig. 1. A similar system is described in US patent 5,187,748 as prior art Fig. la. For example, personal computer systems have been envisaged having fin~ Jlhll identification systems coupled to them for verifying authorised users, before access to a 2 5 computer or collll,uler system is given. For this and other similar applications, it is preferable for the fingel~lilll input device to be, compact, durable, and inexpensive. To this end, it is an object of the invention to provide a fingel~lilll capture device that has relatively few components and that is physically compact, being relatively short in length between the prism to a detecting CCD array.
It is a fu~ther object ofthe invention to provide a relatively inexpensive device that is compact enough to be hand held.
5 Summaly of the Invention It is an object of the invention to provide a fingerprint identification ~paldllls that is compact, relatively in~ ensive and that can focus a fin~e~ l image onto a d~le~;lol with acceptable clarity.
According to the invention, an appd dlus for identifying fingelplillt~ is provided, compri~ing a light source for emitting light;
a ll~l~c;lll prism having a slant surface to which a fingel~lhll being identified is 15 contacted and in which light from the light source is directed for creating a fingerprint lmage;
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism;
a lens spaced between the CCD array and the prism, for focusing light received from the 2 o prism onto the CCD so that an image can be detected; and, diaphragm means disposed between the lens and the prism for preventing some of the light prop~g~ting from the prism in the direction of the lens, from reaching a portion of the lens about its outer edge.
2 5 In accordance with the invention there is further provided, a hand held device for C~lulillg finy,~ll,lhll~, comprising:
a light source for emitting light;
a l1~LS1~e11l prism having a slant surface to which a fin~ lhll being identified is contacted and in which light from the light source is directed for creating a fingel~lh 3 o image;
2 1 ~9200 .~
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism;
a lens spaced between the CCD array and the prism, for focusing light received from the prism onto the CCD so that an image can be detected; and, 5 only a diaphragm disposed between the lens and the prism for preventing some of the light prop~g~ting from the prism in the direction of the lens, from reaching a portion of the lens about its outer edge.
0 Brief Description of the Drawings Exemplary embo-liment~ of the invention will now be described in conjunction with the drawings, in which:
5 Fig. 1 is a prior art side elevation of an embodiment of an appaldlus for identifying finge~
Fig. 2 is a side elevation of an embodiment of an apparatus according to the invention;
2 o Fig. 3 is a side elevation of yet another embodiment of an apparatus according to the mvenhon;
Fig. 4 is a side elevation of a lens having an opaque coating about its periphery depicting a p~ d embodiment of this invention; and, Fig. 5 is a front view of the lens having a coating in the form of a fixed diaphragm applied to are area of the face of the lens as is shown in Fig. 4 in accordance with the inventlon;
3 o Fig. 6 is a co~ ,ulel rendered drawing of a hand held finge~ scanner for connection to a personal computer; and, 21 g9200 Figs 7 and 8 are top and side views respectively of the computer rendered drawing shown in Fig. 6.
Detailed Description Referring now to Fig. 1, a schematic view shows the construction of a representative embodiment of a known type of optical a~paldlus. This ~p~dlus 0 comprises a light source 1 and a diffuser la for emitting a light beam to the subject fingerprint "P". A triangular prism 2 includes a slant surface 2a of about 45 degrees inclination angle on which the fingerprint "P" is laid. An image producing lens system 3 is provided for receiving the reflected light beam from the valleys of the subject fingerprint laid on the prism 2 and then producing an image of the subject finge~
5 "P" at an area charge coupled device 4 ~lelnarl~l, referred to simply as "the area CCD") for converting the produced fingerprint image into an electric signal; theapp~dlus further includes an amplifying/analysing circuit 5 (signal processing circuit) for amplifying then analysing the electric signal for the subject finge,~lin~ provided by the area CCD 4, and a monitor 6 for displaying the fingcll,lilll image shown. The 2 o Ll~clll triangular prism 2 can be made of glass or another suitable material. Other prism shapes such as polygonal e.g. tetragonal may also be employed. The index of refraction of the prism m~teri~l iS preferably in the range of about 1-2.
The prism 2 has a fingerprint receiving face 2a, upon which a finger is placed 25 (indicated by fingerprint P). A fin~,el~l;lll viewing face 16 is disposed at an acute angle, typically of about 45-50, to the fingerprint receiving face 2a. This permits a larger viewing surface and a sharper viewed image than prior art devices. Two opposed parallel faces are perpendicular to the fingcl~ ll receiving face 2a.
3 o In the embodiment of Fig. 1, the light source 1 is in the form of a multi-light emittin~ diode(LED) array, although other conventional light sources could be used. A
suitable LED array is one ofthe type described in US Patent 5,210,588 as comprising a number of high intensity ultra-luminescence chips, which provides a light intensity of about three times that of common LEDs. The disclosure of this Patent is incorporated herein by reference.
Referring now to Fig. 2, an embodiment of the invention is shown wherein a diaphragm is placed at the focal point of the lens to increase the depth of field and to lessen ~ e~i~n distortion. In ~llem~)ling to shorten the distance "d" between the prism 2 and the CCD detector 4 to achieve a more compact device, optical limitations of 10 conventional fingell"hll arrangements such as the one shown in Fig. 1 become more exaggerated and hence, more limiting. For example, as the distance "d" is decreased, the depth of field within of the system decreases; thus the focusing requirements become more stringent. This of course places increased limits on acceptable tolerances of the optical components and their respective placement. Conversely, as the depth of field 15 increases, the task of focusing a fingerprint image on a CCD array becomes less complex. One aim of this invention is to provide a compact, easy to assemble andm~ lf~r,tme fingerprint device. At the same time, it is also pl~felled to lessen the cost of such a device by using a relatively inexpensive, commercially available optical lens or optical lens arrangement. It should be noted, that the diaphragm 5, shown in Fig. 2 has 2 o an extremely small opening. In fact, it is unlikely that this opening would provide enough light for the CCD array to detect an image; however, in theory, it is pl~r~lled to have a small fixed opening with the provlso that enough light be present at the CCD
array to detect a suitable image. If the depth of field is not increased sufficiently to cover the difference in path lengths between D1 and D2 (see Fig. 1), the CCD 4 can be tilted 2 5 to more sharply focus of the image.
Referring now to Fig. 3, a symmetric bi-convex lens is shown exhibiting (3~ 11 optical distortion. As can be seen from the figure, light travelling through the lens at varying distances from the optical axis (various f-ray numbers) does not does not 3 o focus at the same point on the paraxial image plane. This aberration can cause light from a same feature area within a fingel~ ll being imaged, to fall on more than one pixel of the CCD, causing the print imaged by the CCD to appear blurry or out of focus. More costly achromat lenses are available which correct for this problem, however this significantly adds to the cost of m~nllf~ctllre of the fingerprint device. Constraining the light to within a smaller radius about the centre of the lens, i.e. elimin~tin~ low ray f-5 numbers results in a significant improvement in image quality detectecl by the CCDarray. The diaphragm 5 shown in Fig. 3 ess~nti~lly blocks out light from re~hing the outer periphery of the lens, and reduces the (J~ si~n distortion of the inexpensive bi-convex lens 3. Thus, the provision of the diaphragm 5 both increases the field of view and reduces distortion at the lens edge. Of course the amount of light received by the 0 CCD is reduced by blocking some of it with the diaphragm 5, therefore the amount of light about the finger resting on the prism must suff1cient for adequate detection by the CCD. The location of the diaphragm or aperture is important and is related to the size of the ~llule. A large ap~,lult;, allowing light to reach the entire pl~r~ d useable po-rtion of the lens, could be located on the lens or 2 focal distances away. Smaller apertures 5 would need to be placed closer to the focal point based on linear ratio. Thus, an aperture halfthe size ofthe large aperture would ideally be located between 0.5 focal lengths and 1.5 focal lengths from the lens. Locating such an a~ellule outside these distances would result in some loss of information. The simplest form of acceptable ap~llul~ would be an opaque surface or coating applied directly to the outer portion of the lens 2 as is shown 2 o in Figs. 4 and 5.
Referring now to Figs. 4 and 5, a very short and compact device is shown in accordance with a preferred embodiment of the invention. Conveniently, the device is compact enough to be packaged into a hand held instrument about the size of a 2 5 co~ ul.,l mouse, for ~tt~çhment to a personal conl~ , wherein many commercially available devices are several times larger. A lens 5 is disposed between a prism 2 and CCD 5. A diaphragm 5 in the form of a coating, decal, or paint is applied to theperiphery of the lens 3, thus obviating the requirement shown in previous embodiments of this invention, for precisely positioning a diaphragm between the lens and the prism.
3 o Furthermore, by applying the diaphragm directly to the lens, there is no longer a requirement for ~ffixing and holding in place a discrete diaphragm component. Only the lens 3 need be held in place between the CCD 4 and the prism 2.
The system geometry shown in Fig. 4 has proven to work sllcces~fully, producing ~ul~ ially clear images at the CCD 4. A plano-convex lens 3 is used having a focal length of approximately 6 mm. The CCD array 4 has a pixel element size of approximately l0 x l0 ~lm. The iris diameter of the diaphragm was selected to be l mm.
The ~ nce from the lens face to the prism back face is approximately S cm. The distance from the lens to the CCD face is approximately l cm. Preferably, the CCD is tilted as shown at an angle of 5 with respect to the lens back face.
Figs 6, 7, and 8 show the ergonomically ~lesi n~l hand held device that containsthe cil~;uil~.y shown in the previous figures. By reducing the length of the optical path in the manner shown, this small hand held device is realizable and may be m~nllf~tured at a relatively low cost, using an inexpensive lens.
Although white light may be used, it is preferable to employ a monochromatic light source. Red light of a wavelength in the range of 700-800 nm is most pler~ lled, since this wavelength range is at the highest response region of the conventional electronic im~ging devices used. Illumination in the range of 0.5 to 2.5 lux has been found to be effective.
Of course, numerous other embot1iment~ may be envisaged without departing from the spirit and scope of the claimed invention.
It is a fu~ther object ofthe invention to provide a relatively inexpensive device that is compact enough to be hand held.
5 Summaly of the Invention It is an object of the invention to provide a fingerprint identification ~paldllls that is compact, relatively in~ ensive and that can focus a fin~e~ l image onto a d~le~;lol with acceptable clarity.
According to the invention, an appd dlus for identifying fingelplillt~ is provided, compri~ing a light source for emitting light;
a ll~l~c;lll prism having a slant surface to which a fingel~lhll being identified is 15 contacted and in which light from the light source is directed for creating a fingerprint lmage;
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism;
a lens spaced between the CCD array and the prism, for focusing light received from the 2 o prism onto the CCD so that an image can be detected; and, diaphragm means disposed between the lens and the prism for preventing some of the light prop~g~ting from the prism in the direction of the lens, from reaching a portion of the lens about its outer edge.
2 5 In accordance with the invention there is further provided, a hand held device for C~lulillg finy,~ll,lhll~, comprising:
a light source for emitting light;
a l1~LS1~e11l prism having a slant surface to which a fin~ lhll being identified is contacted and in which light from the light source is directed for creating a fingel~lh 3 o image;
2 1 ~9200 .~
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism;
a lens spaced between the CCD array and the prism, for focusing light received from the prism onto the CCD so that an image can be detected; and, 5 only a diaphragm disposed between the lens and the prism for preventing some of the light prop~g~ting from the prism in the direction of the lens, from reaching a portion of the lens about its outer edge.
0 Brief Description of the Drawings Exemplary embo-liment~ of the invention will now be described in conjunction with the drawings, in which:
5 Fig. 1 is a prior art side elevation of an embodiment of an appaldlus for identifying finge~
Fig. 2 is a side elevation of an embodiment of an apparatus according to the invention;
2 o Fig. 3 is a side elevation of yet another embodiment of an apparatus according to the mvenhon;
Fig. 4 is a side elevation of a lens having an opaque coating about its periphery depicting a p~ d embodiment of this invention; and, Fig. 5 is a front view of the lens having a coating in the form of a fixed diaphragm applied to are area of the face of the lens as is shown in Fig. 4 in accordance with the inventlon;
3 o Fig. 6 is a co~ ,ulel rendered drawing of a hand held finge~ scanner for connection to a personal computer; and, 21 g9200 Figs 7 and 8 are top and side views respectively of the computer rendered drawing shown in Fig. 6.
Detailed Description Referring now to Fig. 1, a schematic view shows the construction of a representative embodiment of a known type of optical a~paldlus. This ~p~dlus 0 comprises a light source 1 and a diffuser la for emitting a light beam to the subject fingerprint "P". A triangular prism 2 includes a slant surface 2a of about 45 degrees inclination angle on which the fingerprint "P" is laid. An image producing lens system 3 is provided for receiving the reflected light beam from the valleys of the subject fingerprint laid on the prism 2 and then producing an image of the subject finge~
5 "P" at an area charge coupled device 4 ~lelnarl~l, referred to simply as "the area CCD") for converting the produced fingerprint image into an electric signal; theapp~dlus further includes an amplifying/analysing circuit 5 (signal processing circuit) for amplifying then analysing the electric signal for the subject finge,~lin~ provided by the area CCD 4, and a monitor 6 for displaying the fingcll,lilll image shown. The 2 o Ll~clll triangular prism 2 can be made of glass or another suitable material. Other prism shapes such as polygonal e.g. tetragonal may also be employed. The index of refraction of the prism m~teri~l iS preferably in the range of about 1-2.
The prism 2 has a fingerprint receiving face 2a, upon which a finger is placed 25 (indicated by fingerprint P). A fin~,el~l;lll viewing face 16 is disposed at an acute angle, typically of about 45-50, to the fingerprint receiving face 2a. This permits a larger viewing surface and a sharper viewed image than prior art devices. Two opposed parallel faces are perpendicular to the fingcl~ ll receiving face 2a.
3 o In the embodiment of Fig. 1, the light source 1 is in the form of a multi-light emittin~ diode(LED) array, although other conventional light sources could be used. A
suitable LED array is one ofthe type described in US Patent 5,210,588 as comprising a number of high intensity ultra-luminescence chips, which provides a light intensity of about three times that of common LEDs. The disclosure of this Patent is incorporated herein by reference.
Referring now to Fig. 2, an embodiment of the invention is shown wherein a diaphragm is placed at the focal point of the lens to increase the depth of field and to lessen ~ e~i~n distortion. In ~llem~)ling to shorten the distance "d" between the prism 2 and the CCD detector 4 to achieve a more compact device, optical limitations of 10 conventional fingell"hll arrangements such as the one shown in Fig. 1 become more exaggerated and hence, more limiting. For example, as the distance "d" is decreased, the depth of field within of the system decreases; thus the focusing requirements become more stringent. This of course places increased limits on acceptable tolerances of the optical components and their respective placement. Conversely, as the depth of field 15 increases, the task of focusing a fingerprint image on a CCD array becomes less complex. One aim of this invention is to provide a compact, easy to assemble andm~ lf~r,tme fingerprint device. At the same time, it is also pl~felled to lessen the cost of such a device by using a relatively inexpensive, commercially available optical lens or optical lens arrangement. It should be noted, that the diaphragm 5, shown in Fig. 2 has 2 o an extremely small opening. In fact, it is unlikely that this opening would provide enough light for the CCD array to detect an image; however, in theory, it is pl~r~lled to have a small fixed opening with the provlso that enough light be present at the CCD
array to detect a suitable image. If the depth of field is not increased sufficiently to cover the difference in path lengths between D1 and D2 (see Fig. 1), the CCD 4 can be tilted 2 5 to more sharply focus of the image.
Referring now to Fig. 3, a symmetric bi-convex lens is shown exhibiting (3~ 11 optical distortion. As can be seen from the figure, light travelling through the lens at varying distances from the optical axis (various f-ray numbers) does not does not 3 o focus at the same point on the paraxial image plane. This aberration can cause light from a same feature area within a fingel~ ll being imaged, to fall on more than one pixel of the CCD, causing the print imaged by the CCD to appear blurry or out of focus. More costly achromat lenses are available which correct for this problem, however this significantly adds to the cost of m~nllf~ctllre of the fingerprint device. Constraining the light to within a smaller radius about the centre of the lens, i.e. elimin~tin~ low ray f-5 numbers results in a significant improvement in image quality detectecl by the CCDarray. The diaphragm 5 shown in Fig. 3 ess~nti~lly blocks out light from re~hing the outer periphery of the lens, and reduces the (J~ si~n distortion of the inexpensive bi-convex lens 3. Thus, the provision of the diaphragm 5 both increases the field of view and reduces distortion at the lens edge. Of course the amount of light received by the 0 CCD is reduced by blocking some of it with the diaphragm 5, therefore the amount of light about the finger resting on the prism must suff1cient for adequate detection by the CCD. The location of the diaphragm or aperture is important and is related to the size of the ~llule. A large ap~,lult;, allowing light to reach the entire pl~r~ d useable po-rtion of the lens, could be located on the lens or 2 focal distances away. Smaller apertures 5 would need to be placed closer to the focal point based on linear ratio. Thus, an aperture halfthe size ofthe large aperture would ideally be located between 0.5 focal lengths and 1.5 focal lengths from the lens. Locating such an a~ellule outside these distances would result in some loss of information. The simplest form of acceptable ap~llul~ would be an opaque surface or coating applied directly to the outer portion of the lens 2 as is shown 2 o in Figs. 4 and 5.
Referring now to Figs. 4 and 5, a very short and compact device is shown in accordance with a preferred embodiment of the invention. Conveniently, the device is compact enough to be packaged into a hand held instrument about the size of a 2 5 co~ ul.,l mouse, for ~tt~çhment to a personal conl~ , wherein many commercially available devices are several times larger. A lens 5 is disposed between a prism 2 and CCD 5. A diaphragm 5 in the form of a coating, decal, or paint is applied to theperiphery of the lens 3, thus obviating the requirement shown in previous embodiments of this invention, for precisely positioning a diaphragm between the lens and the prism.
3 o Furthermore, by applying the diaphragm directly to the lens, there is no longer a requirement for ~ffixing and holding in place a discrete diaphragm component. Only the lens 3 need be held in place between the CCD 4 and the prism 2.
The system geometry shown in Fig. 4 has proven to work sllcces~fully, producing ~ul~ ially clear images at the CCD 4. A plano-convex lens 3 is used having a focal length of approximately 6 mm. The CCD array 4 has a pixel element size of approximately l0 x l0 ~lm. The iris diameter of the diaphragm was selected to be l mm.
The ~ nce from the lens face to the prism back face is approximately S cm. The distance from the lens to the CCD face is approximately l cm. Preferably, the CCD is tilted as shown at an angle of 5 with respect to the lens back face.
Figs 6, 7, and 8 show the ergonomically ~lesi n~l hand held device that containsthe cil~;uil~.y shown in the previous figures. By reducing the length of the optical path in the manner shown, this small hand held device is realizable and may be m~nllf~tured at a relatively low cost, using an inexpensive lens.
Although white light may be used, it is preferable to employ a monochromatic light source. Red light of a wavelength in the range of 700-800 nm is most pler~ lled, since this wavelength range is at the highest response region of the conventional electronic im~ging devices used. Illumination in the range of 0.5 to 2.5 lux has been found to be effective.
Of course, numerous other embot1iment~ may be envisaged without departing from the spirit and scope of the claimed invention.
Claims (14)
1. An apparatus for identifying fingerprints, comprising:
a light source for emitting light, a transparent prism having a slant surface to which a fingerprint being identified is contacted and in which light from the light source is directed for creating a fingerprint image;
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism, a lens spaced between the CCD array and the prism, for focusing light received from the prism onto the CCD so that an image can be detected, and, means disposed between the lens and the prism for preventing some of the light propagating from the prism in the direction of the lens, from reaching a portion of the lens about its outer edge.
a light source for emitting light, a transparent prism having a slant surface to which a fingerprint being identified is contacted and in which light from the light source is directed for creating a fingerprint image;
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism, a lens spaced between the CCD array and the prism, for focusing light received from the prism onto the CCD so that an image can be detected, and, means disposed between the lens and the prism for preventing some of the light propagating from the prism in the direction of the lens, from reaching a portion of the lens about its outer edge.
2. An apparatus as defined in claim 1, wherein the means disposed between the lens and the prism is a diaphragm having an opening for allowing some light to pass, and having an opaque portion for preventing light from passing therethrough.
3. An apparatus as defined in claim 2, wherein the diaphragm comprises an opaquematerial covering a portion of the lens about a working area adjacent the optical axis.
4. An apparatus as defined in claim 2, wherein the opening is a fixed opening of a predetermined diameter.
5. An apparatus as defined in claim 2, wherein the diaphragm is disposed about a focal point of the lens.
6. An apparatus for identifying fingerprints, comprising:
a light source for emitting light;
a transparent prism having a slant surface to which a fingerprint being identified is contacted and in which light from the light source is directed for creating a fingerprint image;
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism;
a lens spaced between the CCD array and the prism, for focusing light received from the prism onto the CCD so that an image can be detected; and, means on a portion of a face of the lens about its outer edge for preventing some of the light propagating from the prism in the direction of the lens, from reaching the CCD
array.
a light source for emitting light;
a transparent prism having a slant surface to which a fingerprint being identified is contacted and in which light from the light source is directed for creating a fingerprint image;
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism;
a lens spaced between the CCD array and the prism, for focusing light received from the prism onto the CCD so that an image can be detected; and, means on a portion of a face of the lens about its outer edge for preventing some of the light propagating from the prism in the direction of the lens, from reaching the CCD
array.
7. An apparatus as defined in claim 6, wherein said means is in the form of a substantially opaque coating applied to the periphery of a face of the lens serving as a fixed iris for reducing the unwanted effects of aberration within the lens, and for increasing the depth of field.
8. An apparatus as defined in claim 6, wherein said means is in the form of a decal applied to an area of the lens, about a predetermined preferred working area.
9. An apparatus as defined in claim 6, wherein said means is in the form of a paint applied to an area of the lens.
10. An apparatus as defined in claim 6, wherein said means covers a greater surface area of a face of the lens than an uncovered working portion of the lens on a same face.
11. An apparatus as defined in claim 6, wherein said lens is a plano-convex lens.
12. An apparatus as defined in claim 11, wherein said means is in the form of an opaque iris applied to a face of the lens, and wherein the distance between the CCD array and the lens is less than half of the distance between the lens and the prism.
13. A hand held device for capturing fingerprints, comprising:
a light source for emitting light;
a transparent prism having a slant surface to which a fingerprint being identified is contacted and in which light from the light source is directed for creating a fingerprint image;
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism;
a lens spaced between the CCD array and the prism, for focusing light received from the prism onto the CCD so that an image can be detected, and, only a diaphragm disposed between the lens and the prism for preventing some of the light propagating from the prism in the direction of the lens, from reaching a portion of the lens about its outer edge.
a light source for emitting light;
a transparent prism having a slant surface to which a fingerprint being identified is contacted and in which light from the light source is directed for creating a fingerprint image;
a CCD array disposed a distance from the transparent prism, for receiving an image from the prism;
a lens spaced between the CCD array and the prism, for focusing light received from the prism onto the CCD so that an image can be detected, and, only a diaphragm disposed between the lens and the prism for preventing some of the light propagating from the prism in the direction of the lens, from reaching a portion of the lens about its outer edge.
14. The device as defined in claim 12, comprising means for coupling to a computer port.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60023296A | 1996-02-12 | 1996-02-12 | |
| US08/600,232 | 1996-02-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2189200A1 true CA2189200A1 (en) | 1997-08-13 |
Family
ID=24402811
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2189200 Abandoned CA2189200A1 (en) | 1996-02-12 | 1996-10-30 | Apparatus for identifying fingerprints |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2189200A1 (en) |
-
1996
- 1996-10-30 CA CA 2189200 patent/CA2189200A1/en not_active Abandoned
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